Molecular Simulation Of Properties Change Of Epoxy Resin For Insulator Of DC GIL

With the promotion of energy Internet development strategy and the continuous construction of UHV projects in China,DC GIL will be more widely used in the future.As the key insulation structure of GIL,the failure of epoxy based basin insulator will seriously affect the normal operation of Gil.In this paper,the physical properties,thermal decomposition and adsorption properties of epoxy resin,which is related to the insulation performance,were studied by molecular simulation.The main work and conclusions are as follows:The physical properties of epoxy resin under electric field were simulated by the molecular dynamics method.The results show that the glass transition temperature decreases with the increase of electric field.When the electric field intensity is0.006V/（?）,it is close to the minimum specified in the enterprise standard of State Grid.The thermal conductivity increases slowly with the trend of saturation.The mechanical properties decreased by 20-30%compared with the original The relative permittivity near the center conductor is 15%higher than that at the far end.The tangent of dielectric loss Angle also increases.Further analysis shows that the increase of local electric field strength of epoxy resin will make the local area more prone to charge accumulation,temperature rise and deformation.This will cause the distribution of electric field,temperature field and geometric structure of basin insulator deviate from the optimal parameters determined in the design and affect the insulation performance.The thermal decomposition process and the change of physical properties of epoxy resin were simulated by the reaction molecular dynamics method.It was found that the thermal conductivity of epoxy resin material increased by 63%after the pyrolysis reaction.The mechanical properties of epoxy resin materials decrease beyond the safety margin of the design and the dielectric constant increases by52.63%.This variation was also verified by the variation of the microstructure parameters,such as fractional free volume and cohesive energy density.The analysis shows that the uneven distribution of thermal field will make the local aging speed faster and form the local weak point which is easy to be broken down.In addition,the increase of thermal conductivity enlarges the range of thermal field,which easily leads to the formation of new weak points.The overlapping effect of multiple weak points will significantly reduce the insulation strength of the basin insulatorThe adsorption and diffusion behaviors of various impurity gases in epoxy resin of GIL were simulated by the molecular monte carlo method.It was found that the desorption degree of polar and non-polar molecules is different before and after applying electric field.The results of gas molecular trajectories show that the electric field increases the range of activity of gas molecules by increasing the connectivity between holes in the direction of the electric field.The diffusion coefficient increases correspondingly.This shows that due to the inhomogeneity of the radial electric field distribution of the basin insulator,the distribution of the impurity gas molecules adsorbed by the epoxy resin will overlap,resulting in the increase of the probability density of the local impurity gas molecules.It is further inferred from the simulation results that once the partial discharge occurs on the insulator surface,the impurity gas adsorbed by the insulator will be desorbed and released quickly,thus reducing the concentration and purity of SF₆ gas on the insulator surface.This will lead to the decrease of the insulation performance of the gas-solid interface,and then increase the probability of partial discharge developing into surface flashover.The possible microscopic changes of epoxy resin under Gil condition were studied in this paper.The conclusions can provide theoretical basis and reference for the analysis of the failure causes of epoxy resin based basin insulator.This paper has 48 figures,16 tables,94 references.